The present invention relates to a method of fabricating a variator disc mounted in a toroidal continuously variable transmission.
FIG. 5 schematically shows a variator for use in a full toroidal continuously variable transmission as one type of the toroidal continuously variable transmission mounted in vehicles and the like. The variator 10 includes an input shaft 13 driven into rotation by a vehicular power source 12. The input shaft 13 carries an input disc 15 on respective places near opposite ends thereof. The input disc 15 is formed with a spline hole 15a at its center, the spline hole formed with plural lines of spline grooves. The input disc 15 has the spline hole 15a meshed with a spline shaft 13a of the input shaft 13 so that the input disc is rotated in unison with the input shaft 13 as permitted of a minor movement axially of the input shaft 13. The reason for permitting the movement of the input disc 15 is to apply a required load to an end of the variator 10 by, for example, biasing the right-hand input disc 15 toward the left-hand input disc 15, as seen in the figure, by means of a hydraulic cylinder 17 connected with a hydraulic power source 16. The input disc 15 is formed with a concave race 15b on one side surface thereof.
An output portion 18 of the variator 10 is relatively rotatably carried on an axially central portion of the input shaft 13. The output portion 18 includes an output member 19 and a pair of output discs 20 integrally rotatably carried on the output member 19. The output disc 20 is formed with a concave race 20b on one side surface thereof in face-to-face relation with the race 15b of the input disc 15. The output member 19 is formed with a sprocket gear 19a on its periphery, the sprocket gear meshed with a power transmission chain 23. Three disc-like rollers 21 are interposed between the race 15b of the input disc 15 and the race 20b of the output disc 20 in face-to-face relation. The rollers 21 are in rolling contact with the races 15, 20b, as arranged with equal circumferential spacing. Each of the rollers 21 is rotatably carried by a carriage 22, which is adapted to adjust a position of the roller 21 relative to the races 15b, 20b. 
Thus, the variator 10 is configured as a so-called double cavity type which includes a pair of sets, each of which consists of the input disc 15, output disc 20 and rollers 21. The variator is arranged such that the input discs 15 transmit torque to the output discs 20 via the six rollers 21. The variator is adapted to vary the speed of rotation (transmission gear ratio) of the output discs 20 by adjusting the positions of the six rollers 21 by means of the carriages 22 (See the two-dot chain line in FIG. 5).
The input disc 15 is formed from, for example, a bearing steel. The input disc is generally fabricated by the steps of heat treating a blank for hardening, the blank formed with the spline hole 15a and the concave race 15b by machining; and then finishing the race 15b by machining or grinding using an inside periphery (surface of minimum inside diameter) of the spline hole 15a as a working reference.
In the variator 10, the individual rollers 21 must evenly contact the races 15b, 20b of the discs 15, 20 at high contact pressure in order to ensure the torque transmission between the input discs 15 and the output discs 20.
However, it is difficult to finish the race 15b of the conventional input disc 15 with high precisions because in the process for finishing the race 15b after the heat treatment, tooth flanks of the spline hole 15a, which are used as the working reference, suffer heat-treatment deformation. In addition, assembly precisions of the input disc 15 with respect to the input shaft 13 depend upon the precisions of fitting the spline hole 15a of the input disc 15 on the spline shaft 13a of the input shaft 13. Hence, the working precisions or the heat-treatment deformation of the spline hole 15a and such will result in a problem such as an inclined axis of the race 15b relative to the axis of the input shaft 13 or the like. Thus, the assembly precisions of these elements are decreased. Accordingly, there occurs misalignment between a center of the curvature of the race 15b of the input disc 15 and that of the race 20b of the output disc 20, thus resulting in the following problems. That is, a particular roller 21 is subjected to such a high contact pressure that the roller 21 and the race 15b are decreased in durability. Otherwise, a particular roller 21 is subjected to a decreased contact pressure, so that the torque transmission becomes unstable. Furthermore, there occurs a so-called uneven contact in which a contact surface between the spline hole 15a and the spline shaft 13a is limited to a particular area. This also results the decreased durability of these elements.
As a solution to these problems, it may be contemplated to precisely finish the tooth flanks of the spline hole 15a by electrical discharge machining after the heat treatment. Unfortunately, however, this approach has another problem of low productivity and high fabrication costs.
It is an object of the invention to provide a method of fabricating a variator disc which favorably ensures the precisions of the race with respect to the input shaft and which features high productivity and low fabrication costs.
It is another object of the invention to provide a method of fabricating a variator disc which provides the high-precision finishing of the spline hole.
In accordance with one aspect of the invention, a method of fabricating a variator disc for use in a variator of a toroidal continuously variable transmission, the disc having a concave race on a side surface thereof for rolling movement of rollers and including a spline hole centrally thereof to be meshed with a spline shaft of an input shaft, the method comprises the steps of: forming a concave race with a machining allowance on a side surface of an annular material; forming the spline hole through a blank formed with the race; heat treating the blank for hardening the same; and in a state where the disc is retained by the input shaft, the spline shaft of which is meshed with the spline hole of the disc after the heat treatment of the blank, finishing an outer periphery of the disc using the input shaft as a working reference, and then finishing the race using the resulting outer periphery as a working reference (claim 1).
According to the method of fabricating the variator disc, the precisions of the race with respect to the input shaft are favorably accomplished because the outer periphery of the disc finished using the input shaft as the working reference is used as the working reference for finishing the race. Therefore, the individual rollers are allowed to evenly contact the race such that the durability of the race and rollers is ensured and that the stable torque transmission is carried out. Furthermore, the method accomplishes higher productivity and lower fabrication costs than a case where the spline hole is finished by electrical discharge machining.
In accordance with another aspect of the invention, a method of fabricating a variator disc for use in a variator of a toroidal continuously variable transmission, the disc having a concave race on a side surface thereof and including a spline hole centrally thereof to be meshed with a spline shaft of an input shaft, the method comprises the steps of: forming a concave race with a machining allowance on a side surface of an annular material: forming the spline hole through a blank formed with the race; heat treating the blank for hardening the same; and in a state where the disc is retained by the input shaft, the spline shaft of which is meshed with the spline hole of the disc after the heat treatment of the blank, finishing the race using the input shaft as a working reference (claim 2).
According to the method of fabricating the variator disc, the precisions of the race with respect to the input shaft are favorably accomplished because the race is finished using the input shaft as the working reference. Therefore, the individual rollers are allowed to evenly contact the race such that the durability of the race and rollers is ensured and that the stable torque transmission is carried out. Furthermore, the method accomplishes higher productivity and lower fabrication costs than the case where the spline hole is finished by the electrical discharge machining.
In accordance with still another aspect of the invention, a method of fabricating a variator disc for use in a variator of toroidal continuously variable transmission, the disc having a concave race on a side surface thereof for rolling movement of rollers and including a spline hole centrally thereof to be meshed with a spline shaft of an input shaft, the method comprises the steps of: forming a concave race with a machining allowance on a side surface of an annular material; forming the spline hole with a machining allowance through a blank formed with the race by means of a broach; heat treating the blank for hardening the same; finishing tooth flanks of the spline hole by means of a broach after the heat treatment of the blank; and finishing the race using the finished tooth flanks of the spline hole as a working reference (claim 3).
According to the method of fabricating the variator disc, the tooth flanks are increased in the precisions because the spline hole is formed by means of the broach before the heat treatment of the blank, and after the heat treatment, the tooth flanks are finished by means of the broach. This permits the race to be finished with high precisions using the tooth flanks of the spline hole as the working reference. Therefore, the precisions of the race with respect to the input shaft are favorably accomplished such that the individual rollers are allowed to evenly contact the races. As a result, the durability of the race and rollers is ensured while the stable torque transmission is carried out. In addition, the method accomplishes higher productivity and lower fabrication costs because the tooth flanks are precisely finished by means of the broach. Furthermore, the uneven contact between the spline hole and the spline shaft is relieved so that the durability of these elements is increased, as well.